A spokeswoman for the New York state Department of Agriculture and Markets said Friday that rodent poison was found in tainted pet food that killed several animals and sparked a nationwide recall.

A spokeswoman did not identifying the chemical or its source, beyond saying that it's rodent poison. State officials will be releasing laboratory findings later today. A news conference is expected at 1 p.m. EDT, and you can watch live on wnbc.com.

ABC News reported that the chemical was aminopterin, which was on wheat imported from China.

Various online medical sources indicate that aminopterin is also used in trials to treat leukemia.

March 23, 2007 â€” ABC News has learned that investigators have determined that a rodent-killing chemical is the toxin in the tainted pet food that has killed several animals.

A source close to the investigation tells ABC News that the rodenticide, which the source says is illegal to use in the United States, was on wheat that was imported from China and used by Menu Foods in nearly 100 brands of dog and cat food.

Watch "World News" for full details on the extent of the poisoning.

A news conference is scheduled for this afternoon by experts in Albany, N.Y., where scientists at the state's food laboratory made the discovery a week after a massive recall of 60 million cans and pouches was issued.

The chemical is called aminopterin.

What investigators can't say so far is whether this is the only contaminant, if it is in all of the recalled food, or if it's in enough quantity in to sicken more animals.

There is some good news according to the source. Knowing the chemical should aid veterinarians who are treating animals that have been sickened by the pet food.

Aminopterin is used in the United States in, of all things, a cancer drug, according to the source.

For a week, investigators have been looking for a cause behind the 15 confirmed pet food deaths tied to contaminated pet food. Many animal doctors, including those at New York's Animal Medical Center, suspect there will be a much larger rash of cases after they learned about an additional 200 reported cases of kidney failure in animals.

Doctors at the hospital, which is considered the Mayo Clinic of veterinary medicine, say they noticed the kidney failure while studying sick animals from last Friday to Monday, and traced the cases back to the 60 million cans and pouches of recalled food from Menu Food.

"I was shocked and surprised â€” acute kidney failure is not a common problem," veterinarian Cathy Langston told ABC News. "I've already heard about 200 cases, and so I bet that there are probably going to be thousands."

So far, the government and the pet food maker, which sells food under 91 brand names, have confirmed 15 deaths. But the investigation to locate the toxic contaminant that caused the kidney failure in animals had not pointed to a cause until today.

"This is very much like finding a needle in a haystack," Don Smith of the Cornell Veterinary School said earlier this week. "We're going to keep working at this until we find the cause."

Investigators had already begun looking at the possibility that a pesticide or chemical may have been on the wheat used to produce the Menu Foods dog and cat food.

The Food and Drug Administration, which was notified of the tainted food one day before the recall, said it's frustrated and realizes the growing crisis is an emotional one.

"This is tragic," said Stephen Sundolf of the FDA's Veterinary Medicine group. "It is certainly uncommon. We expect pet food to be safe."

And it's a crisis, if the New York hospital is right, that may not end for weeks.

"I'm worried that there are more deaths to come from chronic renal failure over the next several months," Langston said. "It's not over."

There's a fine line between genius and insanity. I have erased this line.

ALBANY, New York (AP) -- Rat poison has been found in pet food blamed for the deaths of at least 16 cats and dogs, a spokeswoman for the State Department of Agriculture and Markets said Friday.

The toxin was identified as aminopterin, state Agriculture Commissioner Patrick Hooker said in a statement. Aminopterin is used to kill rats in some countries but is not registered for that use in the United States, according to the Environmental Protection Agency.

The officials did not say how they believed it got into the pet food. (Watch why devastated pet owners are suing )

The substance was found at a level of at least 40 parts per million in tested cat food samples, according to Donald Smith, dean of Cornell University's College of Veterinary Medicine.

Aminopterin, also used as a cancer drug, is highly toxic in high doses. It inhibits the growth of malignant cells and suppresses the immune system.

The Food and Drug Administration has said the investigation was focusing on wheat gluten in the food. Wheat gluten itself would not cause kidney failure, but the common ingredient could have been contaminated by heavy metals or mold toxins, the FDA said.

State and FBI officials said they knew of no criminal investigations in the case.

The pet deaths led to a recall of 60 million cans and pouches of pet food produced by Menu Foods and sold throughout North America under 95 brand names. There have been several reports of kidney failure in pets that ate the recalled brands, and the company has confirmed the deaths of 15 cats and one dog.

Menu Foods last week recalled "cuts and gravy" style dog and cat food. The recall sparked concern among pet owners across North America. It includes food sold under store brands carried by Wal-Mart, Kroger, Safeway and other large retailers, as well as private labels such as Iams, Nutro and Eukanuba.

Menu Foods is majority owned by Menu Foods Income Fund of Streetsville. The company also makes foods for zoo cats, but those products are unaffected by the recall.

The company's chief executive and president said Menu Foods delayed announcing the recall until it could confirm that the animals had eaten its product before dying. Two earlier complaints from consumers whose cats had died involved animals that lived outside or had access to a garage, which left open the possibility they had been poisoned by something other than contaminated food, he said.

Menu Foods planned a media teleconference for later Friday, a spokesman said.

A spokesman for New York Attorney General Andrew Cuomo said he was not aware of any criminal investigation involving the tainted food. FBI spokesman Paul Holstein in Albany said Friday he was not aware of any FBI involvement in the case.

"I don't know where we'll go from here," he said.

A complete list of the recalled products along with product codes, descriptions and production dates was posted online by Menu Foods. The company also designated two phone numbers that pet owners could call for information: (866) 463-6738 and (866) 895-2708.

There's a fine line between genius and insanity. I have erased this line.

ALBANY, New York (AP) -- Rat poison was found in pet food blamed for the deaths of at least 16 cats and dogs, but scientists said Friday they still don't know how it got there and predicted more animal deaths would be linked to it.

Also Friday, the company that produced the food expanded its recall to include all 95 brands of the "cuts and gravy" style food, regardless of when they were produced.

The substance in the food was identified as aminopterin, a cancer drug that once was used to induce abortions in the United States and is still used to kill rats in some other countries, state Agriculture Commissioner Patrick Hooker said. (Watch why devastated pet owners are suing Video)

The federal government prohibits using aminopterin for killing rodents in the United States. State officials would not speculate on how the poison got into the pet food, but said no criminal investigations had been launched.

The pet deaths led to a recall of 60 million cans and pouches of dog and cat food produced by Menu Foods and sold throughout North America under 95 brand names. Some pets that ate the recalled brands suffered kidney failure, and the company has confirmed the deaths of 15 cats and one dog.

The company expanded the recall -- which initially covered only cans and pouches of food packaged from December 3 through March 6 -- after the FDA alerted it that some products remained on store shelves.

There is no risk to pet owners from handling the food, officials said.

The Food and Drug Administration has said the investigation into the pet deaths was focused on wheat gluten in the food. The gluten itself would not cause kidney failure, but it could have been contaminated, the FDA said.

Bob Rosenberg, senior vice president of government affairs for the National Pest Management Association, said it would be unusual for the wheat to be tainted.

"It would make no sense to spray a crop itself with rodenticide," Rosenberg said, adding that grain shippers typically put bait stations around the perimeter of their storage facilities.

Scientists at the New York State Animal Health Diagnostic Center at Cornell University and at the New York State Food Laboratory tested three cat food samples provided by the manufacturer and found aminopterin in two of them. The two labs are part of a network created after the September 11 terrorist attacks to keep the nation's animals and food supply safe.

"Any amount of this product is too much in food," Hooker said.

Aminopterin is highly toxic in high doses. It inhibits the growth of malignant cells and suppresses the immune system. In dogs and cats, the amount of aminopterin found -- 40 parts per million -- can cause kidney failure, according to Bruce Akey, director of Cornell's diagnostic center.

"It's there in substantial amounts," Akey said.

Donald Smith, dean of Cornell's veterinary school, said he expected the number of pet deaths to increase. "Based on what we've heard the last couple days, 16 is a low number," Smith said.

Aminopterin is no longer marketed as a cancer drug, but is still used in research, said Andre Rosowsky, a chemist with the Dana Farber Cancer Institute in Boston.

Rosowsky speculated that the substance would not show up in pet food "unless somebody put it there."

Paul Henderson, chief executive of Ontario, Canada-based Menu Foods, said the company does not believe the food was tampered with because the recalled food came from two different plants, one in Kansas, one in New Jersey. Menu continues to produce food at the two plants.

The company, already facing lawsuits, said Friday it is testing all the ingredients that go into the food.

"We have a lot of work to do, and we are eager to get back to it," Henderson said. "This is a highly unusual substance."

A complete list of the recalled products along with product codes, descriptions and production dates was posted online by Menu Foodsexternal link. The company also designated two phone numbers that pet owners could call for information: (866) 463-6738 and (866) 895-2708.

There's a fine line between genius and insanity. I have erased this line.

This is just ridiculous & PROOF that the pet food industry does NOT test their products!! Why aren't batch tests done? The human food industry has to test batches quite regularly. We have a USDA inspector come by quite often & test the food that we produce at the commissary for shipment to our stores & for Internet sales. So, how many batches are pet food manufactures required to test? Is it a one time thing? This is 3 MOTNHS worth or manufacturing! I certainly hope that the plublic demands something be done about this & that requirements & testing proceudres are put into place.

There's a fine line between genius and insanity. I have erased this line.

Everything we've heard in Quebec (also from our Medi-Cal, Hill's and Royal Canin representatives at the clinic, which would technically know what they're talking about) is that a new source for wheat gluten would be the cause of some vitamin overdose, which would cause kidney failure... Either way, this is really bad.